Abstract
The quality is compared of chicken breasts frozen with an electromagnetic freezer (EMF;-45°C, 20, 30 and 40 Hz frequency), a conventional rapid freezer (CRF;-45°C) and a slow freezer (SF;-20°C). Each frozen sample was stored for one week or six months, at -30°C for the EMF-frozen and CRF-frozen samples, and at -20°C for the SF-frozen samples. After thawing and steaming, the weight loss and the rupture stress and strain were examined, and muscle tissues were observed with an optical microscope, transmission electron microscope and cryo-scanning electron microscope. After one week of storage, no difference in drip loss and fracture properties was apparent among the samples that had been frozen by the three freezing methods. However, after six months of storage, the rupture stress of the thawed and steamed samples frozen by SF and CRF had increased. Large spaces were also observed in the muscle fibers of the CRF-frozen samples. These changes might have been caused by protein denaturation during freezing and storing. Such changes as these were clearly suppressed in the samples frozen by EMF. The roundness value of the cross-sectioned muscle fibers of the EMF-frozen samples indicated better freezing effects than in the CRF-frozen samples. It is therefore considered that electromagnetic freezing is more suitable for the prolonged preservation of chicken breasts than conventional rapid freezing.
